Study on the Optical and Gas Sensing Properties of Eu-Doped ZnO

In this work, Eu-doped ZnO columnar films were prepared by a SCS (chemical synthesis from solution) approach, with different doping concentrations, denoted as Eu2 (0.1 at.% Eu) and Eu4 (0.2 at.% Eu). The morphological and optical properties were analyzed by SEM (scanning electron microscopy), transmittance spectra, and responsivity spectra. By increasing the Eu doping concentration, a decrease in transmission was observed, which was also confirmed by the responsivity spectra, which showed a higher responsivity for Eu4 than for the Eu2 sample. Due to the shallower penetration depth of shorter wavelengths, higher responsivity can be observed for 280 nm UV illumination than for other higher wavelengths. The gas sensing properties have been studied for the Eu2 sample which shows a good response to 100 ppm VOC gases at $300{ }^{\circ} \mathrm{C}$. UV sensing properties of the columnar films have been investigated at different temperatures and the results show that higher Eu doping concentration significantly improves the optical performances.